Qfyilyi

A long time ago, I wanted to solve the problem where I would typeset my homework assignments, but copy the file "hw1.tex" to make "hw2.tex", and forget to change the title "Homework 1" at the top of the page.

So I wrote a function (that now I no longer 100% remember how it works, or maybe I got parts of it from a place like StackExchange and never did fully understand it):

usepackage{substr}

newcommand{hwnum}{BehindSubString{hw}{scantokensexpandafter{jobnamenoexpand}}}

Now I can make Homework hwnum the title. When I compile "hw1.tex", the title is "Homework 1", and when I compile "hw2.tex", the title becomes "Homework 2".

Minimal working example (assuming you first save it as a file with the appropriate name):

documentclass{article}



usepackage{substr}

newcommand{hwnum}{BehindSubString{hw}{scantokensexpandafter{jobnamenoexpand}}}



begin{document}



This is Homework hwnum.



end{document}

These days, I have to typeset more than just homework assignments, so I'd like to have this be a bit more flexible.

1. It would be nicer, though not very important, if I didn't have to change the prefix "hw" in the command if I want to deal with filenames such as "day1.tex", "day2.tex", and so on.


2. What I really want is to extract more than one number: for example, "Lecture 7" and "Chapter 3" (or whatever) from a filename such as "ch3lec7.tex".


3. Putting these together, an ideal function would just be able to locate all the numbers in the filename, no matter which non-numbers they're separated by. The same function could pull out 3 and 7 whether it's given the filename "ch3lec7.tex" or "week3day7.tex".

What is a way for me to do at least #2, but also if possible #1 or #3?

The code below uses regular expressions from LaTeX3 to extract all of the numbers in the filename and then makes them available as misha{1}, misha{2}, .... There is no error checking so, for example, if you have misha{100} in your document then this command will fail silently, doing nothing.

If you save the code below as the file ch3lec7.tex then run it you will get the output:

Here is the code:

documentclass{article}



usepackage{expl3}

ExplSyntaxOn

cs_generate_variant:Nn regex_extract_all:nnN {nVN}

seq_new:N l_misha_seq

regex_extract_all:nVN {d+} c_sys_jobname_str l_misha_seq

newcommandmisha[1]{seq_item:Nn l_misha_seq {#1}}

ExplSyntaxOff



begin{document}



   Chapter misha{1}, lecture misha{2}.



end{document}

The work is all done by the command regex_extract_all:nVN, which puts all of the numbers in jobname into an internal LaTeX3 sequence. (As egreg pointed out, LaTeX3 stores the filename in the string constant c_sys_jobname_str.) The command misha{k} prints the kth element of this sequence.